1. Field of the Invention
The present invention relates to a method and apparatus for changing a serving base station in a mobile communication system.
2. Description of the Related Art
In order to maintain optimal performance when data is transmitted in a DownLink (DL) to a User Equipment (UE), a mobile communication system determines which Base Station (BS) can provide the highest quality DL among current serving BSs of the UE and BSs included in the active set of the UE, as the final serving BS of the UE. With regard to this, the active set represents a set of BSs that can provide DL/UpLink (UL) service to the UE.
In general, after the final serving BS is determined, the BS with the highest DL quality may be changed to a BS other than the serving BS due to environmental changes, such as movements. Accordingly, the UE periodically measures the DL quality value for each of its serving BS and the BSs included in the active set, and transmits the measured DL quality values to the serving BS, the neighbor BSs, and a Radio Network Controller (RNC). Based on the transmitted DL quality values, the RNC then determines to maintain or change the current serving BS such that the corresponding UE is served by a serving BS with the highest DL quality value.
In a mobile communication system, DL data service is provided by assigning shared resources to a plurality of users. The DL shared resources are assigned based on DL quality values that are measured and reported in the UpLink (UL) by each UE. That is, a UE reporting a relatively high DL quality value for its serving BS is assigned more resources, and a UE reporting a relatively low DL quality value for its serving BS is assigned fewer resources than the UE having a serving BS with a higher DL quality value. This is because, even if the UE having a serving BS with a relatively low DL quality value is assigned more resources, the possibility that the assigned resources are transferred to the UE is low.
However, there may be a situation where an RNC cannot receive DL quality values, which are measured and transmitted by a specific UE, when a UL quality value for the serving BS of the specific UE is not high. In such a case, since the RNC cannot exactly determine DL quality values for the specific UE, it assigns a small amount of resources to the specific UE regardless of a DL quality value for the serving BS of the specific UE. This causes a problem in that the specific UE cannot be provided with a data service having good quality.